Protein/Calorie Malnutrition
It is generally agreed on that feed can be withheld from healthy, “nonstressed” adult individuals for 2 to 3 days. The average, healthy adult horse or ruminant can apparently tolerate food deprivation (protein/calorie malnutrition [PCM] or simple starvation) for 72 hours with few systemic effects.
In humans a decline in blood glucose concentration results in a fall in insulin concentration. During the first hours to days of starvation, glycogen stores are mobilized from various tissues (liver, kidney, muscle) for glucose production. As glucose becomes limited, many body tissues begin to rely on fatty acid oxidation and the production of ketone bodies as energy sources. Glycerol produced from lipid degradation, lactate from the Krebs cycle, and amino acids provided from muscle tissue breakdown continue to be used for gluconeogenesis to provide energy to glucose-dependent tissues (central nervous system and red blood cells). This response to starvation correlates with an increase in circulating levels of growth hormone, glucagon, epinephrine, leptin, and cortisol and a decrease in insulin and thyroid hormones. During PCM there is an increased drive to eat and a decrease in energy expenditure. Metabolism slows in an effort to conserve body fuels, and the body survives primarily on fat stores, sparing lean tissue until refeeding occurs.Although similar adaptive responses to PCM can occur in the healthy older foal, the neonate has limited body reserves. The healthy newborn foal should have enough liver glycogen to support energy needs for several hours of life. However, glycogen stores at birth can vary significantly with illness or prematurity. Lack of early nutritional support can result in hypoglycemia or hypothermia and quickly affect the ability to maintain functions and behavior.